System and method for navigating an object

ABSTRACT

One example embodiment relates to a method of navigating an object. The method includes detecting when the object accelerates through the speed of sound and maneuvering the object based on when the object accelerates through the speed of sound. Another example embodiment relates to a system for navigating an object. The system includes a detector within the object. The detector determines when the object accelerates through mach one. The system further includes a guidance system within the object. The guidance system adjusts the flight of the object based on data received from the detector.

TECHNICAL FIELD

Embodiments pertain to a system and method for detecting when an objectaccelerates through mach one.

BACKGROUND

An accurate determination of velocity is critical in order to navigateobjects such as projectiles and missiles to a desired point in space.Existing systems and methods often use a GPS receiver to determinevelocity. However, GPS systems add to the cost of producing projectilesand missiles. In addition, many projectiles and/or missiles are used inapplications where the mission timelines are too short to use GPS.

When GPS or other direct means of measurement (i.e., pressuretransducer, Doppler radar) are unavailable or undesirable for whateverreason, the initial velocity must be estimated in order to properlyoperate a guidance system that navigates the object. One method ofestimating the initial velocity of a projectile or missile is tocharacterize the launch velocity versus the temperature of the object'spropellant charge and/or the launch chamber pressure.

Accurately estimating the velocity is crucial in applications whereprecise navigation is required for long range target engagements withobjects such as guided projectiles, bombs and missiles. One of thedrawbacks with existing systems and methods that estimate velocity isthat the accuracy of these estimates often suffers due to externalconsiderations that cannot be accounted for during actual operation ofthe object. As an example, many known projectiles typically have asubstantial variation in propellant characteristics from round to round.This variation usually causes high variability in exit tube velocity(i.e., up to 10 m/s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example projectile engagement scenario where theprojectile exceeds mach one during flight.

FIG. 2 illustrates a flow diagram of an example method of detecting whenan object accelerates through mach one.

FIG. 3 illustrates example acceleration data that may be collectedduring a flight of an object that accelerates through mach one.

FIG. 4 illustrates an example plot of jerk data that may be created fromthe data shown in FIG. 3.

FIG. 5 illustrates an example plot of the jerk data shown in FIG. 4where the jerk data has been filtered.

FIG. 6 illustrates the example plot shown in FIG. 5 and includes datathat may be used in determining the time at which the object acceleratesthrough mach one.

FIG. 7 shows a plot of a projectile's velocity versus time as measuredby radar as well as results for one example projectile test conductedusing the example systems and methods described herein.

FIG. 8 shows an example system for determining when an objectaccelerates through mach one during flight.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

The systems and methods described herein establish the velocity of amissile or projectile at a point in time by detecting when the missileor projectile accelerates through the speed of sound. In addition, whenatmospheric conditions are known (primarily air temperature) the systemand method may calculate the velocity of the missile or projectile whenthe missile or projectile accelerates through the speed of soundtransition. This information relating to the object's velocity at aspecific point in time may be provided to a guidance system (e.g., anInertial Measurement Unit) on the object which utilizes the informationto navigate the object.

As used herein, an object that accelerates through the speed of soundrefers to a guided projectile, projectile, missile, mortar, bomb, plane,spacecraft or any other device that accelerates through mach one.

FIG. 1 illustrates an example projectile engagement scenario 100 wherethe projectile exceeds mach one during flight. It should be noted thatthe projectile typically accelerates through mach one in the fly-outphase of the projectile engagement scenario.

FIG. 2 illustrates a flow diagram of an example method 200 of navigatingan object. The method 200 includes [201] detecting when the objectaccelerates through the speed of sound and [209] maneuvering the objectbased on when the object accelerates through the speed of sound.

The method 200 may further include [207] calculating the velocity atwhich the object is moving when the object accelerates through the speedof sound. In some embodiments, [207] calculating the velocity at whichthe object is moving when the object accelerates through the speed ofsound includes [214] determining the temperature of an environment thatthe object is traveling through. In addition, the accuracy of thevelocity calculation may be improved by also [214] determining thehumidity, pressure and air density of the environment that the object istraveling through.

The method 200 may further include [204] creating a projected flightplan for the object where the projected flight plan includes an estimateas to how long after launch the object will accelerate through the speedof sound and at what velocity the object will be traveling as the objectaccelerates through the speed of sound. In some embodiments, [209]maneuvering the object based on when the object accelerates through thespeed of sound includes [206] comparing the measured time the objectaccelerates through the speed of sound with the estimated time theobject was supposed to accelerate through the speed of sound.

In addition, [209] maneuvering the object based on when the objectaccelerates through the speed of sound may also include [216] comparingthe measured velocity of the object as the object accelerates throughthe speed of sound with the estimated velocity that the object wassupposed to be traveling when the object accelerated through the speedof sound and adjusting the flight of the object.

In some embodiments, [201] detecting when the object accelerates throughthe speed of sound includes measuring the acceleration of the object(e.g., with an accelerometer). It should be noted that any known methodof measuring the acceleration of the object may be used in the method200.

In the example embodiment illustrated in FIG. 2, [201] detecting whenthe object accelerates through the speed of sound includes (i) [208]computing the jerk of the object during flight based on the measuredacceleration; (ii) [210] filtering the jerk; and (iii) [212] calculatingthe speed of sound transition time based on the filtered jerk.

FIG. 3 shows example acceleration data that may be obtained by anaccelerometer measurement located along the projectile body centerline(i.e., x-axis). The plot shows that the rate of changing acceleration isaltered as the object accelerates through mach one. This alteration isindentified in FIG. 3 as an SoS transition.

FIG. 4 shows a plot identifying the derivative of acceleration (i.e.,jerk) that was calculated based on the data shown in FIG. 3. The jerkprovides an indication as to when the projectile passes through thespeed of sound transition (discussed more below). The jerk may becalculated with a digital difference algorithm. In some embodiments, thejerk may be determined more accurately by selecting the appropriateperiod (m) to determine the jerk. As an example, the period (m) may bechosen to be approximately the number of time samples that are necessaryto transition through the speed of sound.

As shown in FIG. 5, the data in FIG. 4 may be filtered to improve thesignal-to-noise ratio. Improving the signal-to-noise ratio enhances theability to determine jerk within the object and as result improvesaccuracy when calculating the speed of sound transition time. It shouldbe noted that the number of samples may be increased with a higherbandwidth accelerometer and/or higher sampling rate. In someembodiments, a small delay (c/2) is accepted for the added accuracyachieved for speed of sound transition time measurements (T_(Center) andT_(Begin)):

Jerk_Filter(n)=mean(Jerk(n−c/2:n+c/2)).

FIG. 6 shows a proof as to how to empirically develop and verify thespeed of sound transition time and jerk relationship. It can be shownthat the delay T₂ from T_(Begin) to the time of the speed of soundtransition is near constant. In addition, it can be shown that the delayT₁ from T_(Center) to time of the center of the speed of soundtransition is also near constant. In some embodiments, a weightedaverage is developed to minimize any time errors associated withacceleration through mach one such that

T _(SoS)=(W ₁·(T _(Center) −T ₁)+W ₂·(T _(Begin) −T ₂))/(W+W ₂).

As is well known, the speed of sound velocity may be estimated withtemperature only as a variable by using the equation:

V _(SoS)=331.5*√{square root over (1 +T/273.15)}

Pressure, humidity and air density can also be used, if known, for amore accurate calculation of V_(SoS).

FIG. 7 shows a plot of a projectile's velocity versus time as measuredby radar as well as results for one example projectile test. Thecalculated T_(SoS), V_(SoS) have been added to the plot from integratedaccelerometer measurements that are used with the example systems andmethods described herein.

FIG. 8 shows an example system 300 for navigating an object 310. Thesystem 300 includes a detector 320 within the object 310. The detector320 determines when the object 310 accelerates through mach one. Thesystem 300 further includes a guidance system 330 within the object 310.The guidance system 330 adjusts the flight of the object 310 based ondata received from the detector 320.

In some embodiments, the detector 320 is an inertial measurement unit320 that includes an accelerometer which measures acceleration of theobject 310 during flight. It should be noted that the accelerometer ispreferably located along an x-axis of the object 310. In addition, asdescribed above with regard to FIG. 4, the inertial measurement unit 320determines the jerk of the object 310 during flight. The inertialmeasurement unit 320 may then filter the measured jerk (see, e.g., plotshown in FIG. 5) before determining the time when the object 310accelerates through the speed of sound based on the filtered jerk (seeFIG. 6).

Based on the measured time that the inertial measurement unit 320determines the object 310 accelerates through the speed of sound, theguidance system 330 adjusts the flight of the object 310 in order todirect the object 310 to a desired location. It should be noted that insome embodiments, the guidance system 330 may also adjust the flight ofthe object 310 based on a calculated velocity that is obtained from theinertial measurement unit 320 and the calculated speed of sound.Providing the calculated velocity to the guidance system 330 isbeneficial to navigating the object 310 because the speed of soundvaries depending on the temperature, pressure, humidity and air densityof the environment where the object 310 is traveling.

The systems and methods described herein may be used with guidedprojectiles and missiles that attain velocities greater than the speedof sound and are used in relatively long time line missions. The systemsand methods are able to monitor the physical phenomenon of an objectaccelerating through mach one in order to facilitate navigation of anobject by determining the velocity of the object at a point in time(i.e., when the object accelerates through mach one) without using GPSor radar.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

1. A method of navigating an object, the method comprising: detectingwhen the object accelerates through the speed of sound; maneuvering theobject based on when the object passes through the speed of sound. 2.The method of claim 1 further comprising calculating a velocity at whichthe object is moving when the object accelerates through the speed ofsound.
 3. The method of claim 2 wherein calculating the velocity atwhich the object is moving when the object accelerates through the speedof sound includes determining a temperature of an environment that theobject is traveling through.
 4. The method of claim 3 whereincalculating the velocity at which the object is moving when the objectaccelerates through the speed of sound includes determining humidity,pressure and air density of the environment that the object is travelingthrough.
 5. The method of claim 1 further comprising creating aprojected flight plan for the object, the projected flight planincluding an estimate as to how long after launch the object willaccelerate through the speed of sound and at what velocity the objectwill be traveling as the object accelerates through the speed of sound.6. The method of claim 5 wherein maneuvering the object based on whenthe object passes through the speed of sound includes comparing ameasured time when the object accelerates through the speed of soundwith the estimated time the object was supposed to accelerate throughthe speed of sound and adjusting the flight of the object.
 7. The methodof claim 6 wherein maneuvering the object based on when the objectpasses through the speed of sound includes comparing a measured velocityof the object as the object accelerates through the speed of sound withthe estimated velocity that the object was supposed to be traveling whenthe object accelerated through the speed of sound and adjusting theflight of the object.
 8. The method of claim 1 wherein detecting whenthe object accelerates through the speed of sound includes measuringacceleration of the object.
 9. The method of claim 8 wherein measuringacceleration of the object includes collecting data from anaccelerometer within the object.
 10. The method of claim 8 whereindetecting when the object accelerates through the speed of soundincludes computing jerk of the object during flight.
 11. The method ofclaim 10 wherein detecting when the object accelerates through the speedof sound includes filtering the jerk.
 12. The method of claim 11 whereindetecting when the object accelerates through the speed of soundincludes calculating a speed of sound transition time based on thefiltered jerk.
 13. The method of claim 12 wherein maneuvering the objectbased on when the object passes through the speed of sound includescomparing the measured time when the object accelerates through thespeed of sound with the estimated time that the object was supposed toaccelerate through the speed of sound and adjusting the flight of theobject.
 14. A system for navigating an object, the system comprising: adetector within the object, wherein the detector determines when theobject accelerates through mach one; and a guidance system within theobject, wherein the guidance system adjusts the flight of the objectbased on data received from the detector.
 15. The system of claim 14wherein the detector is an inertial measurement unit.
 16. The system ofclaim 15 wherein the inertial measurement unit includes an accelerometerthat measures acceleration of the object during flight.
 17. The systemof claim 15 wherein the inertial measurement unit calculates jerk of theobject during flight.
 18. The system of claim 17 wherein the inertialmeasurement unit filters the jerk measured during flight of the object.19. The system of claim 18 wherein the inertial measurement unitdetermines a time when the object accelerates through mach one based onthe filtered jerk.
 20. The system of claim 19 wherein the guidancesystem adjusts the flight of the object based on the time that theinertial measurement unit determines that the object accelerates throughthe speed of sound.
 21. A guided projectile comprising: a casing; aninertial measurement unit within the casing, wherein the inertialmeasurement unit includes an accelerometer that determines when theobject accelerates through mach one, wherein the inertial measurementunit calculates jerk of the object during flight, filters the jerk andthen determines the time when the guided projectile accelerates throughthe speed of sound based the filtered jerk; and a guidance system withinthe casing, wherein the guidance system navigates the guided projectilebased on the time that the inertial measurement unit determines that theguided projectile accelerates through the speed of sound.
 22. The guidedprojectile of claim 21 wherein the inertial measurement unit calculatesthe velocity at which the guided projectile is moving when the guidedprojectile accelerates through the speed of sound.
 23. The guidedprojectile of claim 22 wherein the inertial measurement unit includesprojected flight plan which includes an estimate as to what velocity theguided projectile will be traveling at when the guided projectileaccelerates through the speed of sound and performs a comparison of thecalculated velocity with the estimated velocity, and wherein theguidance system navigates the projectile based on the comparison. 24.The guided projectile of claim 21 wherein the inertial measurement unitincludes projected flight plan which includes an estimate as to when theguided projectile accelerates through the speed of sound and performs acomparison of the determined time when the guided projectile acceleratesthrough the speed of sound with the estimated time when the guidedprojectile accelerates through the speed of sound, and wherein theguidance system navigates the projectile based on the comparison.